The invention relates to the batchwise preparation of aqueous emulsions which comprise organosilicon compound, emulsifier and water. 2. Description of the Related Art
Silicone emulsions are commercially available as milky white macroemulsions in the form of water-in-oil (w/o) or oil-in-water emulsions and as opaque to transparent microemulsions. The emulsions are mixtures of at least one water-insoluble silane, silicone oil, silicone resin, silicone elastomer, or mixture thereof, at least one emulsifier, and water. For the preparation of the emulsion, these components are mixed with one another and dispersed with the use of, for example, heat and cold, mechanical shearing including that produced by means of narrow gaps in rotor-stator systems, colloid mills, microchannels, membranes, high-pressure homogenizers, jet nozzles and the like, or by means of ultrasound. Homogenizing apparatuses and processes are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, CD-ROM edition 2003, Wiley-VCH Verlag, under the keyword “Emulsions”.
The silicone component of the emulsion can be prepared in an upstream reaction outside the emulsification unit and then dispersed in the emulsification unit. Alternatively, the silicone component of the emulsion can be produced in the emulsification unit itself (in situ preparation). Characteristic of the in situ preparation is that a chemical reaction takes place shortly before, during or shortly after the preparation of the emulsion.
All reactions customary in silicone chemistry, in particular those which lead to an increase in molecular weight, can be used for the in situ preparation or polymerization of the silicone component, for example chain extension or equilibration, polymerization, condensation or polyaddition reactions.
The emulsion polymerization of polysiloxanes having terminal OH groups with the aid of acidic catalysts, for example an acidic surfactant, is described in U.S. Pat. Nos. 6,140,414; 5,726,270; and 5,629,388. In U.S. Pat. No. 5,504,150, a phosphazene is used as the acidic catalyst. The base-catalyzed emulsion polymerization of cyclic polysiloxanes or polysiloxanes having terminal OH groups is described, for example, in U.S. Pat. No. 6,201,063.
Polyadditions or hydrosilylation reactions in emulsion are described, for example, in DE 198 56 075, U.S. Pat. No. 6,057,386 EP 1 135 429, and EP 780 422.
Polymerization reactions in emulsion which lead to branched liquid polysiloxanes are described, for example, in DE 199 60 291, and those which lead to branched elastomeric polysiloxanes are described, for example, in WO 00/34359.
In the preparation of silicone emulsions with the use of shearing, for example, the silicone or a silicone mixture is first mixed with at least one emulsifier and a small amount of water and exposed to high shearing, for example in a rotor-stator mixer having narrow gaps. A w/o emulsion having a very high viscosity forms as a so-called “stiff phase”. The viscosity of this stiff phase is very greatly dependent on the shearing. This stiff phase is then slowly diluted with water to the inversion point. At the inversion point, the w/o emulsion becomes an 0/w emulsion. The formation of the stiff phase and the method of dilution with water to the desired final concentration of the emulsion determine the quality of the emulsion. Quality of the emulsion is to be understood in particular as meaning the particle size, the particle size distribution, the storage stability, and the tolerance of the emulsion to heating and/or cooling, vibrations, change of pH, change of salt content, etc.
The abovementioned preparation of silicone emulsions by means of shearing can be effected batchwise or continuously. The batchwise preparation is described, for example, in EP 579 458 A.